Stemming device for explosive charges



Oct c. o. TAPPAN 2,388,232

STEMMING DEVICE FOR EXPLOSIVE CHARGES Filed May 8, 1941 2 Sheets-Sheet 1ATTORNEY.

Oct. 30, 1945. c, O TAPPAN 2,388,232

STEMMING DEVICE FOR EXPLOSIVE CHARGES Filed May 8, 1941 2 Sheets-Sheet 2INVENTOR; Cfiaries 0. 70? an.

Patented Get. 30, 1945 STS STElVIll/IING DEVICE FOR EXPLOSIVE CHARGESEast Hartford, Conn.

Application May 8, 1941, Serial No. 392,468

8 Claims.

The present invention relates to an improvement in blasting plugs andhas for its principal object an improved means for stemming explosivecharges, in blasting work, in rocks, coal, and similar materials.

In current practice'it is well known to drill holes, in the blasting ofrock, coal and the like and in charging the said holes, the blastingcharge being usually detonated by an electric current, this being theusual practice. It is also current practice to increase the explosiveforce of the blasting charge by stemming the charged hole with a tampingmeans, usually comprised of earth, clay or sand, or a combination ofthese and thus the explosive force exerted when the charge is fired, isgreatly enhanced, in proportion to the tightness of the stemming meansin the charged bore or drill.

With the usual practice, stemming such explosive charges, when tampingwith sand or other similar means, consumes considerable time toaccomplish, prior to the firing of the explosive charge.

In current stemming practice, the plug sometimes lets go and theexplosive force exerted in the rock is partially lost. It has been foundthat if a stemming means is provided that does not let go uponexplosion, the explosive forces created in the blasting hole is verygreatly amplified.

Accordingly, as in the present stemming device, if the said meansapplied to the charged hole is positively engaged in the hole, and doesnot let go at the instant of explosion, a greater mass of rock or coalmay be disrupted with a minimum quantity of explosive material.

It is usually customary, when the high explosive material used isdynamite, which is extremely active and extremely powerful, to fire theexplosive charge by means of a controlled detonator, which is buried atthe bottom of the charged hole.

It is amongst the features of advantage of my present invention toprovide a simple stemming means of a mechanical expanding type, that mayeasily and quickly be applied, with a minimum of time and effort, thesaid device being unitary, and

which. at the instant of explosion automatically increases its expansiveresistance to let down at the instant of explosion. The present tampindevice is simple in construction and easy to apply and it only takes ashort time to install the same over the explosive charge, as it requiresonly a few seconds to place in charge stemming position.

One of the outstanding advantages in addition to the above noted, is theprovision of a blasting plug of the expanding mandrel type wherein thefew assembled parts, which are separate, are held together in operativeand applying position by a simple, flexible and resilient partsretaining means.

Another feature of advantage is that due to the construction of thepresent blasting plug, it may be tamped very easily without any dangerof prematurely exploding the blasting charge.

Another feature of advantage in the present blasting plug is that; inthe case of a misfire, i. e. the non-firing of the detonator, whichsometimes occurs, a secondary charge of explosive may be placed in thehole over the first plug inserted, with another detonator, and a secondplug tamped over the secondary charge, which upon firing of said seconddetonator it causes the original explosive charge to explode. Thislatter desirable function is possible due to the construction of theblasting plug. This practice obviously does away with the necessity ofremoving the original explosive charge, to replace the defectivedetonator with a new one, and then reloading the hole. In other wordsthe present plug obviates a number of time consuming steps both in thestemming of the original firing charge and restemming to explode theoriginal misfired charge by the secondary charge.

The foregoing and other advantages will be apprehended as the hereindescription proceeds and it will be obvious that modifications may bemade in the construction'herein, and the methods involved, withoutdeparting from the spirit hereof, or the scope of the appended claims.

In the drawings,

Fig. 1 is a longitudinal sectional view with parts in elevation thesection being taken along the line l-l of Fig. 2 and showing the generalconstruction of the present improved blasting plug;

Fig. 2 is an outer-end elevation of the plug;

Fig. 3 is a sectional View, partially enlarged, of an explosion bore, asdrilled in the material to be blasted, showing the mode of operation ofthe blasting plug, including the manner of lockin-s the same in the holeto prevent its outward movement at the instant of explosion;

Fig. 4 is a view similar to thatof Fig. 3 being in longitudinal sectionshowing theaction of the device at the instant of explosion;

Fig. 5 is a sectional view of the hole showing the mode of retamping orrestemming and the secondary explosion of a misfired charge, due to thefailure of the original detonator;

Fig. 6 is an inner-end elevation of the plug;

Fig. '7 is a fragmental longitudinal sectional the inner ends 5 ofthe.said segments. rangement is for the purpose permitting inward viewpartly in elevation showing another form of the invention;

Fig. 8 shows a section on the line 8-8 of Fig. 7, looking in thedirection of the arrows of said line;

' Fig. 9 is a longitudinal sectional view showing another form of theinvention;

Fig. 10 is a view similar to Fig. 7, showing a similar form of theinvention;

Fig. 11 show an exaggerated transversevsection of a plug much expanded;

Fig. 12 is a side elevation,.partly, in section,

showing a plug showing a passage space between plug sections; and

Fig. 13 is a side elevation, partly in section, showing another form ofplug in which the passage space between plug sections is closed by otherplug sections.

In Fig. 1 there is shown a preferred form of stemming? device and. it.comprises a centrally located; tapered; mandrel or plug, t,preierabl-ycylindrical in cross-section the. inner larger'end, which isinserted into the drill hole foremost, being provided: with an'extending cylindrical flanged. head 2, the plural. surroundingexpandible members; 3-3'-33 of which are. operated upon b z-"inward oroutward movement oi the tapering: mandrel: land; said members.- compriseplural segmental' sections 3,, as shown: in Fig. 2, the. externalsurfaces ofthese joint segmental sections forming a;v cylinder, whichis. slightly smaller diameter than the bore into which the plug is tnvbe introduced. The.-,centralv apertures: of" the combinedsegments form.a. cylindrical. bore, the; said borebeingtapered to fit upon andcooperate with the tapering plug; portion I when the segments areassembled as in Figs. 1 and 2'; While themandrclt anda'the se ments Itmay be made of any-desired material, they may be. made preferably" of asuitable wood, such as ash, hickory; birchpr-the like.

The segments are held-in. engaged position as shown inFigs- I; and 2byrmean of an outer, preferably cylindrical rubber casing or contoun ing'tube 4, the said'casing holding: the segments in position on the taperedplug I.

The assembly; as: shownin Fig. 1, shows: the inner mandrel I its end:flange? spaced at considerable distance from the inner" ends 5- ofthe-sectors. 3:; and the casingkis extended from the sectors to alsoembrace a portion-0t the outer diameter of the flange 2; thus to holdthe mandrel and flange a certain spaced distance: from Thisarl'ongitudinal movement of the segments to cause expansion thereof;v Asthus described the rubber shield or tube holds the plugin. assembledbore applying condition.

The flanged end 2 of the plug is. provided with a;v diagonal vent. bore(i which is locatedangul'arly to the said flange 2. and emergesattheinner space 1 between the inner face of..the flange 2 and the innerfaces il oilthe. sectors 3'.

The inner faces 5 of thesectors3 are provided witha resilientwasher8,,the purpose of which will be describedlater, in detail.

In the assembly above described the. outer diameter of the blastingplug; as exemplified by the rubber shield 4 issm'aller in diameter thanthe drill bore into which the plug is to be introduced, to. permit of.easy manual introduction of the plug within the bore.

In the use of thepresent device, as shown in Fig. 3, after the explosivecharge G and the detonator, not shown, have been introduced into thedrill bore B, the assembled blasting plug is introduced into the bore Buntil the outer face of the mandrel flange 2 meets the outer end of thecharge G, and then a tamping rod T is introduced intothe outer end. of"the bore B, and moved orpushed gently in the direction of the arrow t,and the segments 3 are then pushed inwardly towards theexplosive chargeG in the direction oi the arrow F thus causing the segments 3 to expandoutwardly in the direction of the arrows H, shown in Fig. 3. This actioncauses the segments to expand in the bore B and to firmly engagetheinner surface of the bore B alliroundthereby causing the blasting plugsegments to firmly engage in the bore B.

limtampingthe blasting plug as above described it isobvious that themandrel flange 2 which is in contact with the explosive charge G cannotbe moved. forwardly and. that. the segments. are therefore causedto-ride onthe mandrelplug l. andthereby cause their expansion as abovedescribed- It is understood that the detonator. for the charge:hasalready beenv placed. in the. bottom of the. hole or bore. 13.Afterwards the explosive charge is placed therein, and. obviously the.detonator itself is. attached to the usual. conducting wires. W whichhave. current. conductive terminalson the exterior ends. thereof; at.the outer ends. external of the bore. Bl whichhave. to pass by theblasting plug and. this is. accomplished without. abrasionof the.conductin wires. W" to the detonator when the. plug isinserted by reasonof, the resilient retaining casing 4 asthedetonator wires W- sink intothe. soft. rubbercasing. without deterioration or short circuitingabrasion.

After the plughas been tamped. in position as described in Fig; 3 theplug will occupy a position in whichit is firmly grippedin the bore Bthe surface of which is usually rough, and thus upon firing of theexplosive charge in bore B asindicated at G, Fig. 4-, the instantexplosive expansion of the. charge G causes two things to happen to theblasting plug which are as follows:

Uponv explosion of the charge G,- li-ig. 4, the fiangedtapering mandrell2 is pushed inwardly into the bore engaged segments-3'; in thedirectionof the arrow by the. force. of the. explosion. and this further. expandsthe segments Sin the. bore. B and. causesa very mucharnplified gripofthesegmentsfi against-the. internalwall of the bore B and at the sametime someof the explosive force enters. into thevent hole 5. andexpansion is'created-"inthe space I causing the shield 4- at theexplosion. end to further firmly engage the wall otthebo-re B asindicated by the arrows'in the. space 6., Fig. 4. Simultaneously withthe explosive action. of charge G of Fig. 4-, some of, the explosion--forces-react on.- top and against the l-ip-y, Fig. 4-,. andas-she-wnbythe arrows f -j in said. figure, saidlip y. is. forced down upon thetopof the mandrel flange 2 and seals the plug, against. outward explosionloss. At the same: instant, the-mandrel t, isiorced towards. the faces 5of the segments 3 to fmther increase the expansive grip. of the segments3 to the bcreB,-. as previously described. The. resilient washer 8,further prevents-back flow of the cxplos'rveforces, at the instant of.explosion-.-

It isobviousirom the description. of the temping of the plug in thebore-B as shown and. dcscribed for Fig. 3: that itreduires alightpressure of the tamping rod'I to cause the segments to primarily expandin the bore B sufficiently for initially stemming the explosive chargeG, and that thereafter the explosionof charge G causes a secondary,immediate expansion of the plug in sit-u.

In Fig. 5 there is shown a furtheradvantageous use of the presentblasting plug, there being two shown in the said Fig. 5 one of which isshown in partial section, and due to the fact that the initial charge Ghas misfired, the charge G remains unexploded and thus it becomesnecessary to devise a modification for causing the explosion of theunexploded charge G, without its removal, and this is accomplished bythe following steps:

A secondary explosive charge G is placed at the outer end of the initialblasting plug, this explosive charge G being also provided with adetonator, such as g, and the wires 10 of the detonator pass externallyof the bore B after which a second plug P is forced on to the secondaryexplosion charge G and the secondary plug P is then tamped in positionover the secondary charge G and the secondary charge is exploded andupon explosion of the secondary charge a flame therefrom is passed inthe direction of the arrows A between the faces of the expanded segments3 and the flame continues to pass on in the direction of the arrowsA-a--h causing an expansion of the inner end of the flexible sleeve 4,such flame passing into the unfired original charge G. Some of the flamealso passes through the vent hole E5, to the unexploded charge G and theaction of this flame conduction from the secondary charge causes theexplosion of the initial charge GJ It will be noted in this action thatthe resilient washer K is thrown over from its seat to permit thepassing of the flame from the secondary charge into the primaryunexploded charge G.

The tube or sleeve 4 may be of rubber or other elastic material. and theprice of rubber is high, the sleeve may be made thinner in order to saveexpense, as shown by the sleeve 4' of Fig. 9, and a thick elastic band4a maybe added, for filling the space between the segments 3 and thewall B of the bore.

The sleeve 6 or i may be omitted entirely as shown in Figs. 10 to 13, ormay be replaced by thin paper 4b around the bands do, the bandsproviding the proper elastic filling around the plug-sections. Thus thethick band may be used around the sleeve or tube d of Fig. 1 and with orwithout the sleeves 4, 4 or 42).

Fig. 11 is an enlarged transverse section across a plug with theproportions exaggerated to show that when the plug is over expanded aswhen used in an oversized bore, the thick band do will compensate forthe lack of roundness of the plug.

When the sections are rammed far inwardly on the mandrel to take care ofa large or oversized bore B", the plug becomes not an exact cylinder,but has larger diameters, as at d, at the longitudinal mid-line of thesection periphery, and smaller diameters d,

section peripheries. In such cases. the thick elastic bands 4a arecompressed to be thinner at 5 40, but remains thickest at 4d, so thatthe space between the peripheries of the segments and the bore iseverywhere filled,'and the plug is held firmly in place.

In the form of the invention of Figs. 7 and 8, two thick elastic bandsdo disposed around the sections 3 hold the sections together, and thewhole is enclosed by a sleeve of thin paper disposed around the bandsand plug, in which form the plug may be used, shipped and sold. A cup-If the sleeve is made of rubber a r with the single thick sleeve at theside edges of shaped disk Ill, I l of fiber or thick paper or othersuitable material has its body part It disposed against the ends of thesegments to fill the spaces therebetween, and provided with a centralopening It received on'the mandrel. Said disk includes a flange llextending inwardly substan: tially against the wall of the bore B andadapted to be forced valve-like against the bore to render the plug gastight against outgoing gases during explosions and adapted to allow hotgases to move inward between flange H and the bore wall during thefiring of an unexploded inner charge as a a result of a misfire asdescribed of Fig. 5.

The body part it of said disk has a small opening l2 (Fig. 8) alinedwith a space 13 between the segments and adapted to receive a rubbertube disposed longitudinally in said space H! and through the opening itand projecting beyond both ends of the plug and adapted to receive andprotect the detonator wires W The flange ll may be provided with a slitcommunicating with the opening i2, through which the tube I3 may bemoved laterally into the opening, if desired.

In the form of invention of Fig. 9, a thin elastic tube i and asurrounding thick elastic band to, hold the sections 3 together andprovide a cushioning gripping surface to engage the wall of the bore. Inorder always to protect the sleeve lip 4 and the band 4a from any chanceof being burnt or disabled by the heat of the explosion of the charge, Imay provide a thin disk I0", M (Fig. 9) of flexible asbestos or othersuitable heat-resistant material having its middle part 10" disposedagainst the head 2 and its margins H" folded back over the end lip 4" ofthe sleeve to protect the latter.

This disk ID", H" may be effectively used 4, or thin sleeve l with orwithout the band 4a.

In the form of invention of Fig. 13, I provide an outer set 311 and aninner set 3b of segmental plug sections, each section having an innerface having a taper slidably received on and substantially correspondingto the taper of the mandrel I, as in Fig. 1, the peripheral faces of thesections of both sets 3a and 3b togetherforming an approximatelycylindrical plug, as shown. Thick elastic bands 4a are disposed aroundthe sections of each set, the sleeves 4 or may also be used.

The end faces of one set ofv sections 3a or St meet the end faces of theother set in a plane perpendicular to the axis of the plug, the sectionsof one set being alined with the spaces l3 between the sections of theother set, thereby to close said spaces l3 to render the plugsubstantially gas-tight during the explosion.

The invention claimed is:

1. A blasting plug including a taper mandrel disposable coaxially of theexplosive-charge-receiving hole and provided at its larger end with aninner flanged head; plug sections each having an inner tapered faceslidable on the mandrel, the sections and mandrel together forming anapproximately cylindrical plug; a resilient tube around the sections andsaid head; the sections being movable inwardly on the mandrel tocompress the tube against the wall of the hole leaving a chamber betweenthe sections and said head, the inner end lip of the tube lying againstthe peripheral face of the head; a resilient washer disposed around theinner end of the mandrel and closing the spaces between the sections;saidhead being provided with an aperture between the chamber and theface of said head at the charge; pressure of the explosive gasespressing said lip onto the head to confine and force the gases againstthe head to force outwardly the mandrel to further expand the sections;said washer and lip serving as a check valve to prevent outward passageof gas during the explosion, and serving to admit the inward passage offlame through said spaces and aperture and around the head, when asecondary charge is exploded at the outer end of the plug, to explode aninner charge that has misfired.

2. A blasting plug for stemming explosive charges in holes drilled inrock, coal or other material, said plug including a taper mandrel ofwood or other suitable material disposable coaxially of the hole andprovided at its larger end With a flanged head large in diameter thansaid larger end but smaller in diameter than the hole and having a flatend face disposable fiat against the explosive charge in the inner partof the hole; a plurality of segmental plug sections of wood or othersuitabl material, each having an inner face having a taper received onand substantially corresponding to the taper of the mandrel, the outerfaces of the sections together forming an approximately cylindrical plugof slightly less diameter than the hole; a cylindrical rubber contouringtube disposed around the sections and said head; the sections beingadapted to be simultaneously rammed rearwardly on the mandrel with atamping rod, to uniformly expand the sections against the contouringtube and compress the latter against the wall of the hole to grip thelatter, leaving an annular chamber between the inner ends of thesections and said head, the inner end lip of the tube lying against theperipheral face of the head and yieldably closing said chamber; a flatresilient washer disposed around the inner end of the mandrel and flatagainst the inner ends of the sections to close the spaces between thesections; said head being provided with an aperture between said chamberand the face of said head at the charge.

3. A blasting plug for stemmin explosive charges in holes drilled inrock, coal or other structure, said plug comprising a taper mandrel; aplurality of segmental plug sections, each having an inner face having ataper slidably received on and substantially corresponding to the taperof the mandrel, the peripheral faces of the sections together forming anapproximately cylindrical plug; one or more thick elastic bands disposedaround the sections; a cup-shaped disk of fiber or thick paper or othersuitable material having its body part disposed against the ends of thesegments to fill the spaces therebetween, and provided with a centralopening received on the mandrel, and with a flange extending inwardlysubstantially against the wall of the bore and adapted to be forcedvalve-like against the bore during explosion.

4. In a plug as in claim 3 the body part of said disk having a smallopening alined with a space between the segments; and a rubber tubedisposed longitudinally in said space and through the Opening, andprojecting beyond both ends of the plug and adapted to receive andprotect the" detonator wires.

5. A blasting plug for stemming explosive charges in holes drilled inrock, coal or other structure, said plug comprising a taper mandrel; anouter and an inner set of segmental plug sec-, tions slidably receivedon the mandrel; end faces of one set meeting the end faces of the otherset in a plane perpendicular to the axis of the plug; the sections ofone set being alined with the spaces between the sections of the otherset.

6. A blasting plug including a taper mandrel disposable coaxially of theexplosive-charge-receiving hole and provided at its larger end with aninner flanged head; plug sections each having an inner tapered faceslidable on the mandrel, the section and mandrel together forming anapprox imately cylindrical plug; a resilient tube around the sectionsand said head; the sections being movable inwardly on the mandrel tocompress the tube against the wall of the hole leaving a chamber betweenthe sections and said head, the inner end lip of the tube lying againstthe peripheral face of the head; and means movable relative to themandrel forming a transverse arcuate bridge at the inner end faces ofthe sections and spanning the spaces therebetween to prevent passage ofgases between the plug sections when the sections are separated by themandrel.

7. A blasting plug disposable coaxially of an explosive-charge-receivinghole comprising a tapered mandrel having on its larger end a flangedhead disposable against an explosive in the hole; longitudinal plugsections on and around the mandrel and each section having an innertapered face slidable on the mandrel, the sections and mandrel togetherforming an approximately cylindrical plug; a stretchable band around thesections to hold the sections and mandrel together; the sections beingmovable toward said head on the mandrel to compress theband against thewall of the hole; and means movable relative to the mandrel forming atransverse arcuate bridge at the inner end faces of the sections andspanning the spaces therebetween to prevent passage of gases between theplug sections when the sections are separated by the mandrel.

8. A blasting plug disposable coaxially of an explosive-charge-receivinghole comprising a tapered mandrel having on its larger end a flangedhead disposable against an explosive in the hole; longitudinal plugsections on and around the mandrel and each section to be enga edagainst an explosive charge; plug sections, each having an inner taperedlongitudinal face in straight line contact with and slidable on themandrel and an end face at right angles to the axis of the mandrel toform a shoulder, the sections and mandrel together forming anapproximately cylindrical plug the sections terminating at their outerend in a common substantially transverse plane; stretchable bindingmeans around the sections; the sections being longitudinally movable onthe mandrel toward the head thereof to compress the means against thewall of the hole; and arcuate means movable relative to the mandrelforming a transverse arcuate bridge at the inner end faces of thesections engaging said shoulders and spanning the spaces therebetween,whereby impact of a tamping rod on the outer end of the plug, will causelongitudinal movement of the sections relative to the mandrel and towardthe head and said shoulders will force the arcuate means along themandrel and prevent the means from being caught concentrically betweenthe tapered faces of the sections and mandrel.

CHARLES O. TAPPAN.

